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標(biāo)題: APUE中線程鎖的問題 [打印本頁]

作者: DNFCF 時間: 2011-04-10 13:48
標(biāo)題: APUE中線程鎖的問題
本帖最后由 DNFCF 于 2011-04-10 13:57 編輯

#include <stdlib.h>
#include <pthread.h>

#define NHASH 29
#define HASH(fp) (((unsigned long)fp)%NHASH)

struct foo *fh[NHASH];

pthread_mutex_t hashlock = PTHREAD_MUTEX_INITIALIZER;

struct foo {
      int          f_count;
      pthread_mutex_t f_lock;
      struct foo    *f_next; /* protected by hashlock */
      int          f_id;
      /* ... more stuff here ... */
};

struct foo *
foo_alloc(void) /* allocate the object */
{
      struct foo       *fp;
      int                      idx;

      if ((fp = malloc(sizeof(struct foo))) != NULL) {
            fp->f_count = 1;
            if (pthread_mutex_init(&fp->f_lock, NULL) != 0) {
                     free(fp);
                     return(NULL);
            }
            idx = HASH(fp);
            pthread_mutex_lock(&hashlock);
            fp->f_next = fh[idx];//
            fh[idx] = fp->f_next;//想不通這兩句是什么意思,第二句貌似是多余的吧？？？求指點
            pthread_mutex_lock(&fp->f_lock);
            pthread_mutex_unlock(&hashlock);
            /* ... continue initialization ... */
            pthread_mutex_unlock(&fp->f_lock);
      }
      return(fp);
}

void
foo_hold(struct foo *fp) /* add a reference to the object */
{
      pthread_mutex_lock(&fp->f_lock);
      fp->f_count++;
      pthread_mutex_unlock(&fp->f_lock);
}

struct foo *
foo_find(int id) /* find an existing object */
{
      struct foo       *fp;
      int                      idx;

      idx = HASH(fp);
      pthread_mutex_lock(&hashlock);
      for (fp = fh[idx]; fp != NULL; fp = fp->f_next) {
            if (fp->f_id == id) {
                     foo_hold(fp);
                     break;
            }
      }
      pthread_mutex_unlock(&hashlock);
      return(fp);
}

void
foo_rele(struct foo *fp) /* release a reference to the object */
{
      struct foo       *tfp;
      int                      idx;

      pthread_mutex_lock(&fp->f_lock);
      if (fp->f_count == 1) { /* last reference */
            pthread_mutex_unlock(&fp->f_lock);
            pthread_mutex_lock(&hashlock);
            pthread_mutex_lock(&fp->f_lock);
            /* need to recheck the condition */
            if (fp->f_count != 1) {
                     fp->f_count--;
                     pthread_mutex_unlock(&fp->f_lock);
                     pthread_mutex_unlock(&hashlock);
                     return;
            }
            /* remove from list */
            idx = HASH(fp);
            tfp = fh[idx];
            if (tfp == fp) {
                     fh[idx] = fp->f_next;
            } else {
                     while (tfp->f_next != fp)
                              tfp = tfp->f_next;
                     tfp->f_next = fp->f_next;
            }
            pthread_mutex_unlock(&hashlock);
            pthread_mutex_unlock(&fp->f_lock);
            pthread_mutex_destroy(&fp->f_lock);
            free(fp);
      } else {
            fp->f_count--;
            pthread_mutex_unlock(&fp->f_lock);
      }
}

代碼中，紅色部分求指點

作者: DNFCF 時間: 2011-04-10 14:25
怎么沒人回一下，給自己頂一下

作者: sjtlqy 時間: 2011-04-10 14:40
我?guī)湍沩斏先?img src="static/image/smiley/default/em02.gif" smilieid="71" border="0" alt="" />

作者: DNFCF 時間: 2011-04-10 14:47
回復(fù) 3# sjtlqy

謝謝

作者: yulihua49 時間: 2011-04-10 17:56

#include
#include

#define NHASH 29
#define HASH(fp) (((unsigned long)fp)%NHASH)

struct foo ...
DNFCF 發(fā)表于 2011-04-10 13:48

環(huán)形鏈表。

作者: lwrsmy 時間: 2011-04-10 18:06
fp->f_next = fh[idx];//
fh[idx] = fp->f_next;//想不通這兩句是什么意思,第二句貌似是多余的吧？？？求指點

確實書中錯了
原意是每次在hash隊列頭部插入下一元素
改為：
fp->f_next = fh[idx]->f_next;
fh[idx]->f_next = fp;

作者: DNFCF 時間: 2011-04-10 18:44

fp->f_next = fh;//
fh = fp->f_next;//想不通這兩句是什么意思,第二句貌似是多余的吧？？？求指點

...
lwrsmy 發(fā)表于 2011-04-10 18:06

贊同�。。�

作者: ydfgic 時間: 2011-04-12 13:40
這兩句寫反了
你自己想想

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